Processing and turnover are being studied in whole cells and in extracts. The pathway of processing and the half-lives of processed segments are followed using subcloned fragments of complementary mouse rDNA. The subcloned fragments are also used to test whether accurate processing cleavages can be made by purified enzymes (including E. coli RNase III and Hela double-stranded RNase), and to assay for the purification of processing activities. Turnover is investigated 1) by studying the mode of action of one possible agent, lysomal RNase, on ribosomes, and 2) by assaying for factors that may regulate the rate of rRNA turnover in whole cells, using a new short-term turnover test and cells with augmented or diminished levels of lysosomal enzymes.